Troubleshooting

The following information assumes direct connection of a piezoelectric acceleration sensor to a sensor amplifier, FFT analyzer, or other such device with a dedicated cable.

 

Signal is not output

 

1. Check that connectors are not loose.

Check for the connection. If it is loose, connect it securely. Insert until rattling of cable-side connector stops.

Note: If a stop washer is attached, a connector may still rattle even when it is inserted securely. Although washers may be excessively flattened, they need to be tightened until rattling stops.

2. Check that cables are not disconnected.

Replace with a spare cable to check. Disconnection can be checked by the disconnection detection function using CCLD if it is the model equipped with the function.

3. Check that CCLD drive is on.

Check the setting of a sensor amplifier/FFT analyzer whether CCLD is on or not. An amperage consistent with sensor specifications must be selected.

Note: Input connections must always be AC. In the CF-7200 analyzer, the CCLD function switches off automatically if the detector is disconnected. So CCLD must be switched on when reconnecting.

4. Check that the NP-0021 miniature/BNC conversion adapter is used or not.

An application including an accelerometer and NP-0021 miniature/BNC conversion connector may have a bad connection because a rubber packing attached to the NP-0021 is too thick to insert firmly. Please use the NP-0021 without rubber packing in that case.

Make sure that a rubber packing should be removed before connection when the NP-3211 is used.

The signal from an accelerometer seems to break off. Sometimes disconnection is detected or there is no signal reception.

 

 

Excessive noise

 

1. Check that cables are not under excessive force.

Attach cables securely, without excessive force applied to cables.

2. Check that cables are steady.

Particularly when using a charge output-type accelerometer, if cables are vibrating and unsteady, the cables themselves produce static electricity noise. Attach securely to prevent vibration.

3. Check that sensors are not placed in a drafty location or in an environment subject to sudden, severe temperature changes, such as proximity to an incandescent light bulb

Sudden, severe temperature changes produce low-band noise (pyroelectric effect) through distortion caused by thermal expansion of the sensor case. Whenever possible, avoid direct exposure to drafts, etc., and avoid exposure to radiant heat from incandescent light bulbs and other heat sources.

4. Check that no ground loops exist
Creation of ground loops readily produces so-called common mode noise. Optimal corrective measures differ depending on the grounding status of the equipment on site. Try the following measures, and use the method that works best.
  1. Securely ground the measurement target, sensor, sensor amplifier, and FFT analyzer (secure grounding will make this method most effective against noise. If factory grounding is poor even when ground leads of all devices are connected to factory ground terminals, ground loop noise may remain).
  2. Disconnect the ground lead of either the measuring system or the sensor amplifier/FFT analyzer (poor grounding can form a ground loop; in such cases, loops can be cut either by interrupting grounding of the measuring system through use of a floating (insulated) type sensor or an insulating stud designed to interrupt a ground loop (available by special order; contact your nearest distributor) or by not grounding the sensor amplifier/FFT analyzer.).
5. Noise current is flowing to the measurement target

Use an insulating stud to prevent noise from flowing to the measuring equipment.

Note: In such cases, the sensor amplifier/FFT analyzer must be grounded reliably. An insulating stud is available by special order. Contact your nearest distributor.

6. The system is affected by motor flux leakage
Try some of the following corrective measures.
  1. Change the location of sensor installation.
  2. Gain some distance with an insulating stud or other structure (An insulating stud is available by special order. Contact your nearest distributor.).
  3. Sensors with built-in amplifiers are susceptible to such effects; switch to a charge output-type sensor.
7. Check that the accelerometer is not exposed to powerful magnetic noise
Try some of the following corrective measures.
  1. Charge output-type sensors transmit signals with high impedance and can easily pick up noise during transmission. Switch to a sensor with a built-in amplifier.
  2. Regardless of the type of sensor used, cables can also act as magnetic noise antennae; change cable orientation or routing.
  3. Use a zipper tube or other structure to shield and ground all wiring.
  4. Do not run wiring parallel to power supply lines. Wire along a separate route, and when crossing cables, cross perpendicularly. Also separate as much as possible.

 

 

Signal amplitudes or acceleration spectra are unusual.

 

1. Acceleration values are unusual
Carefully calibrate the sensitivity of the accelerometer by the FFT analyzer.
2. Check that the mass of the accelerometer is sufficiently small, relative to the work piece

Connecting an accelerometer increases the mass of the work piece (mass effect) and thus lowers its natural frequency. As a guideline, the mass of the sensor should be approximately 1/50 of the work piece mass or less.

Does weight of an accelerometer have influence on the measurement result?

3. Check that the accelerometer is installed correctly

The mounting way of the accelerometer can create differences in frequency characteristics due to a contact resonance effect. Make sure that the sensor is mounted as rigidly as possible.

4. Check that the vibrating axis and the installation surface of the acceleration sensor are perpendicular.

Be aware that oblique attachment of an accelerometer (at a given angle) causes detection of the cosine component of actual vibration and leads to low values.

5. Check that the input range is not exceeded

Check an AD-over, input level indicator, and level indicator on the charge amplifier when using a charge-type accelerometer as well as spectrum or time-axis waveforms of the FFT analyzer to adjust to appropriate levels. Avoid making determinations based on the display of the FFT analyzer alone. Particularly when measuring impact vibration with a compact sensor, the FFT frequency range can be too low, and large vibrations close to the resonant frequency of the sensor can be overlooked. Also take note for instances when large vibrations of several 10-fold kHz or higher are detected.

 

Revised:2010/06/14


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